Degradation of Pesticides - Pesticides: Evaluation of Environmental Pollution - page 56

Another method based on photo-Fenton reaction (Equations 3.6 through 3.8) is

. OH 3 + 2 + +

Fe + → hv Fe + H +

(3.6)

. OH 2 + 3 + −

Fe + H O → Fe + OH +

(3.7)

2 2

. OH Pesticide

+ → Photoproduct

(3.8)

During photodegradation of chemical compounds including pesticides, following types
of photoreactions are possible:

1. Norrish type-I reaction 2. Norrish type-II reaction

R

R CH 3

R

R 1 R 2 R 1 R 2

CH 2

HO

or

CH 2

O

O O O CH 2

H

3. Isomerization (geometrical or optical)
(a) (b)

R 1

H H H CH 3

H 3 C CH 3

H 3 C CH 3

R 1 H 3 C

R 1

R 1

H

H

H H H

H R 1

R 2 R 2 R 2

H H

H 3 C COOR 3 H

R 2

H 3 C R 2 COOR 3

COOR 3

4. Ester cleavage, decarboxylation, decarbonylation

R 1 R 2

R 1

OR 2 R 1 R 2 R 2

R 1 R 1 R 1 O

OR 2 or

R 1 COOH

R 2

or +

O

O O O O

R 2 OH

5. Dehalogenation

CCl 3 CCl 2 CHCl 2

CCl 2

or

ArO OAr ArO OAr ArO OAr ArO OAr

CI·

6. Dealkylation

CH 3

CH 2 OH

CHO

H

R N

R

N

R N R N

H

H

H H